Field of Invention
The present invention is related to a method for producing an apparatus for dispensing a medium, and to an apparatus produced with the method.
Background Information
It is known in the art to fill a cartridge of such an apparatus by front filling the cartridge through an outlet for dispensing the medium. Alternatively, cartridges are often filled through an inlet arranged on a filling side, which is usually arranged at an end of the cartridge that is arranged opposite to the outlet of the cartridge; this is usually called back filling.
Usually, the cartridge and a piston to be received in the cartridge in a movable manner are produced separately with an injection molding process. After production, for the front-filling procedure the piston is inserted into the cartridge and moved to a filling position. In the filling position, a conveying side of the piston for dispensing the medium from the cartridge is in contact with an outlet face of the cartridge; thereby a residual volume can be often formed between the conveying side of the piston and the outlet face.
It is further known in the art as e.g. disclosed in EP 2 428 282 A1 that air can be trapped in the cartridge before or during the filling process. The trapped air can be detrimental inter alia to the dispensing quality and accuracy. Hence, a venting mechanism is often arranged in the piston to remove the trapped air after the filling process.
Although the known solutions for venting trapped air work reliably and effectively, these solutions are sometimes too costly for certain, cost-critical applications. Furthermore, the presence of the venting mechanism sometimes provides a residual volume for air to be trapped, which cannot be removed after the filling.
A prior art method of making a valve of a dispensing device for dental substances is known from WO2012/087631 A1.
The article by Tilo Vaahs titled: “Medizintechnik für den Massenmarkt” (medical technology for the mass marked) published in KU Kunstoffe, Jahrg. 90 (2000) 10, pages 242-244, relates to plastic packaging that can be used for drugs and drug dosage systems, such as insulin. Having regard to medical technology POM and PBT are cited as being suitable in the medical field as packaging materials.
The article by David Raia: “Factors That Affect Performance of Overmolding Bond Strength” published in ANTEC 2011/2527 on Jun. 1, 2011, relates to the overmolding of different components relative to one another and specifies different bond strengths between different materials for specific thermoplastics that can be used as medical equipment housings.
To prevent air to be trapped in the cartridge during the filling process, it is also known in the art to apply a vacuum to the cartridge and subsequently fill the cartridge with the medium. This has the disadvantage of making the filling process more cumbersome and costly.